The present invention relates to the inspection of assembled printed circuit boards (hereinafter "printed circuit board" is abbreviated as "PCB"), and is particularly concerned with the creation of numerical control (hereafter referred to as NC) data for use in a system for visual inspection of electronic components mounted on a PCB.
Conventionally, creation of NC data to be used in an inspection system for assembled PCBs has been carried out by on-line data teaching in the inspection system. To shorten the time needed for such teaching, automatic creation of NC data for inspection has been adopted by using NC data in a mounter which has NC data concerning electronic component locations and by using computer aided design (hereafter referred to as CAD) data created during design of the PCBs. An inspection system of this kind is exemplified in Japanese Patent Application Laid-Open No. 61-107105.
The prior art mentioned above does not handle the relation between the time needed for creating NC data for inspection and an actual PCB, so conventional teaching methods cannot permit the inspection systems to operate during teaching, resulting in the problem that a long time is required for teaching when hundreds of electronic components are mounted on a PCB. Moreover, other conventional methods of using data, such as CAD data, to automatically create NC data for inspection cannot avoid minute gaps between optimum locations and locations provided by such data, necessitating the operator's own checking if automatically created data is applied to actual data for PCBs. This difference between actual PCBs and PCB CAD data is mostly caused during manufacture of the PCBs. On the other hand, the difference between actual data for PCBs and NC data for a mounter arises partly because mounter NC data itself is produced from PCB CAD data and partly because, even if the operator corrects data on his mounter, he cannot make the final fine adjustment with his own eyes.
As for the positional allowance for mounting electronic components, no method of only using NC data on electronic component locations from external systems like data shown above can permit creating data taking into consideration the fact that such a positional allowance is not specified by some numerical value related to an electronic component location but by the forms of soldering pads at the location and by the wiring pattern around the location. Besides, in order to determine where an inspection window for checking a failure, such as solder bridging, which is likely to occur, should be positioned in an image to be inspected or an objective image, it is also necessary to consider the pad and wiring pattern of a PCB. The use of only the above-mentioned NC data on electronic component locations from external systems is not enough for creation of data including such information about PCB pad and wiring patterns. For the above reason, with the prior art, even if NC data for inspection is automatically created by such data as CAD data, it has been necessary to check the automatically created data one by one and also sometimes to add other information with the result that the data creation has taken a very long time.